Esters of polynuclear alcohols and lubricating oils containing same



United States Patent ice ABSTRACT OF THE DISCLOSURE Esters of certain hydroxylated fused ring aromatic compounds, when employed in lubricating oils, impart to those oils improved oxidative and corrosive properties. Broadly, the ester additive is represented by the followin g structural formula:

wherein R and R can be the same or different, and contain from 2 to 20 carbon atoms, preferably 6 to 11 carbon atoms, and are each selected from the group consisting of normal alkyl, branched chain alkyl, aryl, aralkyl, cycloaliphatic, normal alkenyl, branched chain alkenyl, and aralkenyl, the preferred group being normal alkyl and branched chain alkyl groups; n is 0 to 3, preferably 1;

X is a carbonyl or hydroxy group or both; m is 1 to 4; and Ar is a hydrocarbon radical of naphthalene, a hydrocarbon radical of anthracene, or a hydrocarbon radical of phenanthrene, preferably a hydrocarbon radical of anthracene.

BACKGROUND OF THE INVENTION have been widely employed as the base lubricant in these types of jet engines, as they demonstrate better overall stability than mineral oils. For -a description of some of these ester oils, see US. Patents 3,126,344 and 3,282,971. However, at the high temperatures at which these jet engines operate (550 to 650 F. and higher) even these oil compositions are corrosive to the metal surfaces with which they come in contact and, moreover, under extreme heat and exposure to air, these lubricants become oxidatively unstable and break down, leading to viscosity increase and further corrosion.

Most high temperature aviation turbo lubricants contain various additive materials to inhibit corrosivity and oxidation of the lubricant. Quinizarin and other anthraquinone's have been employed in these oils for these purposes and have been described in Canadian Patent 538,935 and US. Patents 2,839,468 and 2,801,968. Previous additive materials, however, have been found to exhibit deficiencies in oxidative stability and corrosion inhibition under high performance operating conditions. New and more effective materials able to meet high performance requirements mustbe employed and are therefore of great importance to the lubricant art.

3,470,099 Patented Sept. 30, 1969 SUMMARY OF THE INVENTION It has now been found that esters of certain hydroxylated fused ring aromatic compounds are extremely effective an anti-corrosion and antioxidation agents in lubricating oils in general and lubricating oils of high performance jet aircraft in particular.

- Broadly, the ester additive is represented by the following structural formula:

wherein R and R can be the same or different and contain from 2 to 20 carbon atoms, preferably 6 to 11 carbon atoms, and are each selected from the group consisting of normal alkyl, branched chain alkyl, aryl, aralkyl, cycloaliphatic, normal alkenyl, branched chain alkenyl, and aralkenyl, the preferred group being normal alkyl and branched chain alkyl groups; n is 0 to 3, preferably 1; X is a carbonyl or hydroxy group or both; ml is 1 to 4, and Ar is a hydrocarbon radical of naphthalene, a hydrocarbon radical or anthracene, or a hydrocarbon radical of phenanthrene. Examples of R and R' include, but are not limited to, ethyl, propyl, butyl, hexyl, octyl, decyl, undecyl, tetradecyl, octadecyl, eicosanyl, isopropyl, isopentyl, 2,2-dimethyl butyl, 3-ethyl-4-methyl-octyl, benzyl, Z-methyl-benzyl, 3-pentyl benzyl, cyclopentyl methyl, cyclohexyl methyl, propenyl, 2-hexenyl, 2-monenyl, 3-undecenyl, 3,3-dimethyl-4-butenyl, 4-methyl-2- pentenyl, 3-benzyl-2-pentyl, 4-benzyl-2-octenyl, etc.

The preferred additive is an ester derivative of a hydroxylated anthroquinone and is represented by the following structural formula:

wherein R is a C to C normal or branched chain alkyl group, preferably the former, and A is selected from the group consisting of H and a C to C normal or branched chain alkyl acyl group, preferably the C to C normal. Examples of R include, but are not limited to, hexyl, octyl, decyl, undecyl, 2,2-dimethyl butyl, and 2,2-dimethyl pentyl, etc. Nonlimiting examples of normal or branched chain alkyl acyl groups include heptoyl, octanoyl, nonanoyl, decanoyl, undecanoyl, 2,2-dimethyl butanoyl and 2,2-dimethyl pentanoyl, etc. Most preferably the additive is a diester of quinizarin which is represented by the structural formula:

0 II III wherein R and R are C to C normal alkyl groups. Examples of R include hexyl, heptyl, octyl, nonyl, decyl and undecyl.

The lubricating compositions of the invention will comprise a major amount of lubricating stock and an amount suflicient to inhibitoil oxidation and corrosion, usually 0.1 to 10 wt. percent, preferably 0.5 to 3 wt. percent, based on the total amount of lubricating composition, of the ester additive.

The lubricating stocks for this purpose may be any natural or synthetic material having the desired lubricating properties or mixtures thereof. The viscosity of these oils may vary over a wide range such as from 100 SUS at 100 F. to 100 SUS at 200 F. The hydrocarbon oils may be blended with fixed oils such as castor oil, lard oil and the like and/or with synthetic lubricants such as polymerized olefins, copolymers of alkylene glycols or aliphatic alcohols with organic acids, e.g., 2-ethylhexyl sebacate, dioctyl adipate, and the like.

Synthetic lubricating bases of the ester or ether type may also be used as a lubricating oil and are preferred. High molecular weight, high boiling liquid aliphatic dicarboxylic acid esters are suitable ester oil bases as they possess excellent viscosity temperature relationships and lubricating properties. Diester and triester synthetic lubricating bases may be appropriately used as the lubricating oil. Specific examples of operable diesters are di-2-ethylhexyl sebacate, di-Z-ethylhexyl azelate, di-Z-ethylhexyl adipate, di-n-amyl sebacate, di 2 -ethylhexyl-n-dodecyl succinate, and di-Z-ethoxyethyl sebacate. Other ester oils suitable as lubricating bases can be found in US. Patents 3,126,344 and 3,282,971. Specific examples include trimethylolpropane tripelargonate, trimethylolpropane tricaprylate, trimethylolpropane tricaproate, trimethylolpropane tri-neo-heptanoate, trimethylolpropane tri-neo-decanoate, trimethylolpropane mono-neo-heptanoate dipelargonate, and combinations thereof.

The esters of this invention may be prepared by reacting a hydroxy-containing aromatic compound having the structural formula:

where X is selected from the group consisting of a carbonyl group, a hydroxy group or both; y is to 4; m is 1 to 4, and Ar is a hydrocarbon radical of naphthalene, a hydrocarbon radical of anthracene, or a hydrocarbon radical of phenanthrene, directly with an appropriate esterifying agent, preferably an acid chloride. Preferably the hydroxy-containing aromatic compound is a hydroxylated anthraquinone, e.g., 1-hydroxy-9,IO-anthraquinone, 2-hydroxy-9,IO-anthraquinone and, most preferably, quinizarin, i.e., 1,4-dihydroxy-9,IO-anthraquinone.

Acid chlorides suitable for reaction with the hydroxycontaining aromatic compounds are C to C preferably C to C normal alkyl, branched chain alkyl, aryl, aralkyl, cycloaliphatic, normal alkenyl, branched chain alkenyl and aralkenyl acid chlorides, the preferred acid chloride being a normal or branched chain alkyl acid t chlorides.

Specific examples of suitable acid chloride include propanoyl chloride, butanoyl chloride, pentanoyl chloride, heptanoylchloride, nonanoyl chloride, undecanoyl chloride, dodecanoyl chloride, pentadecanoyl chloride, nonadecanoyl chloride, uneicosanoyl chloride, isobutanoyl chloride, isohexanoyl chloride, 2,2-dimethyl pentanoyl chloride (neo-heptanoyl chloride), 3-ethyl-4-methyl-nonanoyl chloride, benzoyl chloride, Z-methyl-benzoyl chloride, 3-pentyl benzoyl chloride, cyclopentyl acetyl chloride, cyclohexyl acetyl chloride, 2-butenoyl chloride, Z-heptenoyl chloride, Z-decanoyl chloride, 3-dodecenoyl chloride, 3,3dimethyl-4-pentenoyl chloride, 4-methyl-2- hexenoyl chloride, 3-benzyl-2-hexenoyl chloride, 4-benzyl- 2-nonenoyl chloride, etc. Preferred acid chlorides are C-; to C normal or branched chain alkyl acid chlorides, e.g., heptanoyl chloride, nonanoyl chloride, undecanoyl chloride, dodecanoyl chloride, 2,2-dimethyl pentanoyl chloride, isohexanoyl chloride, etc.

The esters are produced by reacting a hydroxy-containing aromatic compound with an appropriate acid chloride in the presence of an inert solvent, and usually with a catalyst, at elevated temperatures under reflux conditions for a period of time sufficient to carry out esterification, which is usually from about 2 to 76 hours.

The inert solvent is usually a hydrocarbon solvent such as heptane benzene, toluene, xylene, etc. Although a catalyst for esterification is not required, usually one is employed in small amounts. Suitable catalysts are acidic, basic or neutral with the preferred one being an acid catalyst, e.g., sodium acid sulfate, sulfuric acid, p-toluene sulfonic acid, etc. All hydroxy groups of the hydroxycontaining aromatic compounds are not necessarily esterified with the acid chloride, the amount of ester product being controlled by the amount of the acid chloride present in the reaction. Thus, for example, one mole of a dihydroxy starting compound may be reacted with one mole of an acid chloride to produce a monoester containing a hydroxy group.

Recovery of the ester additive is preferably effected by neutralization of the reaction product followed by filtering, distilling, and recrystalling the ester from a polar solvent. Neutralization can be carried out with an organically soluble basic organic or inorganic compound such as 10% aqueous -KOH, amines, etc., the preferred neutralization agent being pyridine. After neutralization the product is filtered to remove impurities and then distilled under a reduced pressure, e.g., 5 to 150 mm. of Hg pressure to remove solvent. The residue left after the distillation, which is the ester, is preferably recrystallized from an organic solvent such as benzene, xylene, toluene, and most preferably from conventional polar solvents such as alcohols, e.g., methanol, ethanol, propanol, etc.; ethers, e.g., dimethyl ether, methylethyl ether, diethylether, etc.; ketones, e.g., acetone, methylethyl-ketone, diethylketone, etc., or esters, e.g., methyl acetate, ethyl acetate, methyl butyrate, etc. Usually a small amount of bone charcoal, e.g., 0.1 to 10 wt. percent, is employed in the recrystallization step as an absorption agent.

The additive of the present invention can be used alone or in combination with other additives in a lubricating oil base. Usually various other additives are added to the lubricant base in amounts of about .001 to 10 wt. percent each, based on the total weight of the composition. Examples of such additives include: rust preventives such as calcium petroleum sulfonate or sorbitan monooleate; viscosity index (V.I.) improvers such as the polymethacrylates; oxidation inhibitors such as diphenylp-phenylenediamine, cyclohexyl p phenylenediamine, phenyl-alpha-naphthylamine, phenyl-beta-naphthylamine, para-amino-diphenylamine, 3,7-dioctyl phenothiazine, p, p'-dioctyl diphenylamine, and phenothiazine; load carrying agents such as tricresyl phosphate and anticorrosion agents such as free sebacic acid; pour point depressants, dyes, grease thickeners and the like.

It is within the contemplation of this invention to prepare additive concentrates in which the concentration of additive is greater than would normally be employed in a finished lubricant. These concentrates may contain in the range of from 10 to 90% of additive on an active ingredient basis, the balance-being a hydrocarbon solvent. Such concentrates are convenient for handling the additive in the ultimate blending operation into a finished lubricating oil composition. The additive concentrates may be made simply of an additive of the present invention in a suitable mineral oil medium or they may include other additives that are intended for use along with the additives of the invention in a finished lubricant.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will be further understood by reference to the following examples:

Example 1 To a 2-liter flask fitted with a thermometer, stirrer and condenser were added 240 grams (1.0 mole) 1,4- dihydroxy-9,lO-anthraquinone (quinizarin), 480 grams (2.2 moles) dodecanoyl chloride (lauroyl chloride), 600 ml. of xylene, and 5 grams of H The reaction mix- 5 ture was stirred at reflux for 8 hours and thereafter cooled to 80 C., whereupon 150 grams of pyridine was added. The mixture was stirred for an additional 2 hours at a temperature between 80 C. and 100 C., then oxy)-9,10-anthraquinone which, for convenience, has been designated as quinizarin dilaurate, were evaluated according to well known oxidation-corrosion stability tests, the results of such tests being shown in Table I.

TABLE I Metals corroded, rug/ch13 Percent A Visc. A Oxidation, corrosion stability tests Cu Mg Fe Al Ag at 100F. T.A.N.

400 F., 72 hours:

011A 1 +0.02 0.00 0.00 +0.01 +0.01 22.3 1. 54 Oil A-lgl pt. by wt. qninizarin d1- 0. 12 0. 0.00 0. 00 0.00 18.4 1.55

a a e 0. 17 -0.05 0.00 0. 00 0. 00 31.4 3.73 450 F., 48 hours:

-0. 18 12. 63 +0.02 0. 01 -0.04 58.5 5. 94 Oil A+1 pt. by wt. quinizarin dilaurate 0. 17 0. 01 0. 00 0.00 0.02 31.5 2.93

1 Oil A is a lubricant composition containing 75 parts by weight of the triester prepared by fully esterifying trlrnethylolpropane with a C35 average n-alkyi carboxylic acid, i.e., esterified with octanoic and nonanoic acids, 25 parts by weight or the ester prepared by iully estenfying dipentaerythritol with a 06 average n-alkyl carboxylio acid, i.e., esterified with to C n-alkyl carb oxylic acids, 1.3 parts by weight p,p-dioctyldiphenylamine 1.1 parts by weight of phenyl-B-naphthylarnine, 1.0 part by weight of tricresyl phosphate, 0.1 part by Weight of quinizarin, 0.025 part by weight of sebacic acid, and 0.001 part by weight of silicone.

cooled and filtered. The filtrate was distilled under a pressure of mm. Hg until a final temperature of 100 C. was obtained. 40 grams of the residue was dissolved in 1,200 ml. of boiling methanol. One gram of bone charcoal was added, the 'mixture filtered, and the filtrate cooled to 0 C. This cooled material was again filtered leaving 36 grams of 1,4-bis(dodecanoyloxy)-9,10- anthraquinone (quinizarin dilaurate) having a melting range of 83.5-85 C.

Example 2 To the apparatus of Example 1 was charged a mixture of 480 grams (2 moles) of purified 1,4-dihydroxy-9,10- anthraquinone (quinizarin), 850 cc. of xylene, and 1 gram of concentrated sulfuric acid. This mixture was then brought to reflux. To this refluxing mixture 300 grams (2 moles) of 2,2-dimethylpentanoyl chloride (neoheptanoyl chloride) was added dropwise with stirring over a 12 hour period. After this addition was completed the reaction mixture was refluxed for a further 40 hour period. The mixture was then cooled to 120 C. and 480 grams (2.2 moles) of dodecanoyl chloride (lauroyl chloride) was added in one portion. Reflux was resumed for a 24-hour period. At the end of this period the reaction mixture was vacuum stripped with the pot temperature maintained at 140 C. The residue was dissolved in 2 liters of boiling hexane containing 30 grams of bone charcoal. This solution was stirred for 30 minutes and filtered. The filtrate was cooled to 0 C., affording 780 grams of crude product. Recrystallization from hexane produced 590 grams of pale yellow colored product having a melting point range of 41 C. to 43 C. Infrared analysis confirmed the product to be 1-[2,2-dimethylpentanoyloxy] 4 dodecyloxy-9,lO-anthraquinone (quinizarin mononeo-heptanoate monolaurate).

Example 3 In the manner of the preceding examples, 240 grams (1 mole) of 1,4-dihydroxy-9,IO-anthraquinone (quinizarin), 475 milliliters of xylene, 1 gram of concentrated H 80 and 330 grams (2.2 moles) 2,2-dimethylpentanoyl chloride (neoheptanoyl chloride) were reacted at the reflux temperatures of the mixture for 48 hours. At the end of this period the reaction mixture was filtered and the filtrate stripped of the excess acid chloride and xylene under 10 mm. Hg vacuum to a pot temperature of 100 C. The residue was dissolved in 500 ml. of boiling hexane and chilled to 0 .C. This material was then filtered by suction filtration leaving 395 grams of 1,4-di-[2,2- dimethylpentanoyloxy] 9,10 anthraquinone (quinizarin di-neo-heptanoate) having a melting point of 137 to 140 C.

The anticorrosive properties of the l,4-bis(dodecanoyl- The oxidation corrosion stability tests referred to in Table I were carried out by blowing air at the rate of volumes per hour through 1 volume of ester maintained at the indicated temperature for the indicated periods of time. Thus, in the 425 F., 72-hour oxidationcorrosion-stability test, the ester was maintained at a temperature of 425 F. for a period of 72 hours. These tests simulate to a degree the operating conditions of jet engines. The percent increase in centistoke viscosity, metals corroded, and the increase in total acid number (T.A.N.) were then determined. The effectiveness of the quinizarin ester was evaluated in combination with other additives conventionally employed in a fully finished lubricant.

As seen by the data of Table I, the additives of this invention were very effective in inhibiting oxidation and corrosion at higher temperatures. The lubricant containing the fused ring aromatic ester of this invention was substantially less corrosive than the lubricant containing no such compound. The percent change in viscosity and change in total acid number are smaller when the additive of this invention is employed, thus indicating the antioxidant properties of the substance.

What is claimed is:

1. A lubricating oil composition comprising a major amount of lubricating oil and a minor amount suflicient to improve the oxidation and corrosive characteristics of the oil of an additive represented by the following structural formula:

O /\/\4 l ll kA g where A is selected from the group consisting of H and a C to C alkyl acyl group and wherein R is a C to C alkyl group.

2. The lubricating oil composition of claim 1 wherein the additive is further characterized as having the following structural formula:

wherein R and R are C to C alkyl groups.

3. The lubricating oil composition of claim 2 wherein R and R are C alkyl groups.

4. A compound having the formula:

wherein R and R are C to C alkyl groups.

5. The compound of claim 4 wherein R and R are C alkyl groups.

6. An additive concentrate comprising from about 10 wt. percent to about 90 wt. percent of a hydrocarbon solvent and from about 90 wt. percent to about 10 Wt. percent of the compound of claim 4.

7. A process for preparing the compound of claim 4 which comprises (a) reacting quinizarin with a sufiicient amount of a C to C alkyl acid chloride in an 20 inert solvent under reflux conditions in the presence of anacid catalyst for a period of time sufficient to elfect substantially complete esterification of said quinizarin and (b) recrystallizing the ester product of step (a) from a polar solvent.

8. The process of claim 7 wherein the polar solvent is a C to C alkyl alcohol.

References Cited UNITED STATES PATENTS 2,194,478 3/ 1940 Moser et al 252-57 2,430,857 11/1947 Borsoif et al. 25257 X 2,607,746 8/1952 Magoffin 252-404 2,906,780 9/1959 Hirschmann et al. 260410.5 X 3,294,836 12/1966 Peterson et al. 260475 PATRICK P. GARVIN, Primary Examiner W. CANNON, Examiner US. Cl. X.R. 

